Tuesday, April 13, 2010

ActionScript: Dynamic Streaming

There's an article here about dynamic streaming in Flash Media Server 3.5 using Flash 10's new QoS features. It's a three-part series, and I just spent several hours reading it.

It talks about a class that Adobe provides called "DynamicStream". It doesn't come with ActionScript 3.0--it's a separate download. I was hoping to integrate this class into JW Player in order to do more intelligent bitrate switching using Adobe's new QoS features.

Let me explain why I'm frustrated.

First of all, this article was a three-part series, each with several pages. Hence, it was very long--much longer than I think was necessary. Part 3 covered "Integrating dynamic streaming with existing video players". Since it was the final page in the entire series, I expected it to be very exciting and useful. Instead, it was very mediocre. I can summarize, "Hey, this stuff doesn't work in Flash 9, so you'll have to do something else to support older players. Here, read this long code sample to learn how to parse the Flash player version number." There's a lot of code like:
private function _verifyServerVersion( p_version:String ):void
var fmsVersion:Number = Number( p_version.split(",", 2).join(".") );

trace("fmsVersion: " + fmsVersion);

if ( fmsVersion >= _targetFMSVersion )
_isServerCapable = true;
_isServerCapable = false;
At the very least, that if/else could have been written:
_isServerCapable = (fmsVersion >= _targetFMSVersion);
However, I think it's a flaw in ActionScript that you have to parse the version numbers manually at all.

Next up, I looked at the DynamicStream class, and it had multiple different coding styles:
if (...) {
if(...) { ... }
When I see stuff like that, I lose my confidence in the code. The file is 1049 lines long, by the way.

Having said all that, what really frustrates me is that the code doesn't take into consideration the widths for the various encodings. Currently, JW Player will pick the best encoding based on width and bitrate. That way, you can have different encodings for different size players. This is important for several reasons. First of all, there's no use pulling down an HD video for a 480x320 player until the user goes full-screen. It eats up bits that could be going to quality instead of size. Furthermore, it's better to avoid scaling on the client since it looks better to scale only once during encoding.

Hence, I'm more than a little disappointed by the DynamicStream class, and I'm stuck wondering how the heck I'm going to pull the useful bits out of this 1049 line file in order to integrate them into JW Player. Ugh, painful.

Oh, did I mention Silverlight takes care of bitrate switching entirely automatically? Double ugh.

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